This invention relates to a toner supply device provided with a conveyance path extending from a mount position of a toner cartridge to an outlet in communication with a developing device, and adapted for supplying toner from the toner cartridge to the developing device through the conveyance path.
There have been available image forming apparatuses such as copying machines and printers in which an electrostatic latent image formed on a photosensitive member is developed with two-component developer including toner and carriers. In these image forming apparatuses, a space is defined between a frame of a main body and a cover so as to provide an operation lever or the like for maintenance. In some image forming apparatuses, a toner cartridge is provided in this space so as to make the size of the apparatus smaller.
In these image forming apparatuses, there are provided a toner conveyance path extending from the toner cartridge to a developing device, and a conveying member in the form of a spiral. The conveying member is disposed in the toner conveyance path and is drivingly rotated by a drive motor. The toner from the toner cartridge is designed to fall onto the toner conveyance path spontaneously, and the fallen toner is conveyed by the conveying member up to a toner outlet provided at a downstream side of the conveyance path. The toner is discharged to the developing device through the toner outlet.
After the existing image forming apparatus is installed at a specified place, the developing device is filled with developer having a suitable toner density. Further, a toner cartridge for supplying toner to the developing device when the toner density of the developer decreases below a given level is mounted at a toner cartridge mount portion. At this time, the toner falls onto the toner conveyance path spontaneously and is accumulated at a portion of the conveyance path right below the mount portion.
Thereafter, the toner density decreases as the toner in the developing device is consumed after the start of an image forming operation. The toner density is detected by a toner sensor, and the drive motor is driven in accordance with a sensor signal output from the toner sensor. Thereby, the toner accumulated on the conveyance path right below the cartridge mount portion is conveyed to the toner outlet by the conveying member.
However, the toner density in the developing device remains in the low level until the toner reaches the toner outlet and is supplied to the developing device. Thus, the image forming operation is obliged to continue in a state where the toner density is low until the toner density increases up to an appropriate level, and accordingly images cannot be formed properly.
Further, if the image forming operation is conducted continuously while the toner is conveyed to the toner outlet, the toner density in the developing device decreases further. When the toner density decreases as low as a toner empty level, a toner empty indication is displayed despite the fact that there still remains toner in the toner cartridge.